Silver transfer diffusion process

ABSTRACT

Silver transfer images having improved highlights are obtained by using silver halide emulsions wherein the silver halide is substantially completely in the form of grains having a diameter of at least 0.5 micron.

United States Patent [1 1 Young SILVER TRANSFER DIFFUSION PROCESS [75] Inventor: Richard W. Young, Norfolk, Mass.

[73] Assignee: Polaroid Corporation, Cambridge,

Mass.

22 Filed: Apr. 1, 1971 21 Appl. No.: 130,383

[52] US. Cl. 96/29 R, 96/76 R, 96/95 [51] Int. Cl G031: 5/54 [58] Field of Search 96/107, 29, 109.

[56] References Cited UNITED STATES PATENTS 3,687,677 4/1972 Audran et a1 96/109 2,662,822 12/1953 Land 96/29 Oct. 16, 1973 4/1962 Oliver 96/94 3/1970 Illingsworth 96/107 OTHER PUBLICATIONS Photographic Science and Engineering, Vol. 5, No. 6, November-December 1961, pp. 332-336 Primary ExaminerNorman G. Torchin Assistant Examiner-John L. Goodrow AttorneyBrown & Mikulka [5 7] ABSTRACT 24 Claims, 3 Drawing Figures PMENTEU [1U 16 I975 sum 1 0F 3 v I N VENTOR. RICHARD W. YOUNG 6 mm TORN E YS PATENIED OCT 16 I975 .765889 SHEET 2 OF 3 INVENTOR.

A TORNEYS PATENIEUucnsnm 3.765889 SHEET NF 3 INVENTOR. RICHARD W. YOUNG EW maxim AT ORNEYS SILVER TRANSFER DIFFUSION PROCESS This invention relates, in general, to diffusion transfer photography and, more particularly, to silver diffusion transfer processes.

The copending application of Edwin H. Land, Ser. No. 675,472 filed Oct. 16, 1967 (now U. S. Pat. No. 3,671,241 issued June 20, 1972), discloses and claims silver diffusion transfer processes employing imagereceIving elements which comprise an image-receiving stratum of regenerated cellulose containing a silver precipitatinG agent. The image-receiving stratum is obtained by alkaline hydrolysis of a cellulose ester, e.g., cellulose diacetate, containing a silver precipitating agent. Only a depthwise portion of the cellulose ester stratum need be hydrolyzed to regeneratd cellulose. The transferred silver is precipitated within the regenerated cellulose stratum thus obtained, even though an additional depthwise portion of the cellulose ester may be hydrolyzed to cellulose during the diffusion transfer process and additional silver precipitating nuclei thus made available.

This invention is concerned with an improvement in diffusion transfer processes employing such imagereceiving elements. A primary object of this invention is to provide diffusion transfer processes employing regenerated cellulose silver-receptive strata wherein the silver transfer image exhibits improved highlights.

A further object of this invention is to provide silver diffusion transfer processes, and products useful in performing such processes, wherein the photosensitive silver halide emulsion contains silver halide grains of specified character whereby improved silver transfer images may be obtained.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and the relation and order of one or more of such steps with respect to each of the others, and the products possessing the features, properties and the relation of elements which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description, taken in connection with the accompanying drawing wherein:

FIG. 1 reproduces a graph of the grain size distribution of a silver halide emulsion found to be useful in accordance with this invention and compared with a control silver halide emulsion;

FIG. 2 reproduces graphs of the grain size distribution, area and volume of a silver halide emulsion found useful in accordance with this invention; and

FIG. 3 reproduces graphs of the type shown in FIG. 2 and plotted with respect to a control silver halide emulsion.

Diffusion transfer processes are now quite well known and their details need not be repeated here. In a silver transfer process, for example, a photoexposed silver halide material and a silver precipitating material are subjected to an aqueous alkaline solution comprising at least a silver halide developing agent and a silver halide solvent. The developing agent reduces exposed silver halide to silver and the solvent reacts with unreduced silver halide to form a complex silver salt that migrates to the silver precipitating material where it is precipitated or reduced to form a visible silver image.

As indicated above, said copending Land application discloses diffusion transfer processes employing imagereceiving elements prepared by incorporating a silver precipitating agent in an alkali-impermeable polymer or polymeric material to provide a dispersion wherein said silver precipitating agent constitutes the inner phase of said dispersion. The resulting dispersion is then coated as a layer on a support and subjected to appropriate hydrolysis treatment to convert at least a depthwise portion of said alkali-impermeable polymer to an alkali-permeable polymer. If the hydrolyzed polymer in which the silver transfer image is formed is water-insoluble, as in the case of regenerated cellulose obtained by hydrolysis of cellulose diacetate, the resulting transfer image may be subjected to washing without danger of physical damage, the washed print exhibiting high gloss and exceptional stability characteristics. These methods and the advantages obtained thereby are set forth in detail in said Land application.

This invention is concerned with improvements in diffusion transfer processes employing image-receiving elements of the type described in said Land application, and to improve the photographic and optical properties of the silver transfer image formed in said image-receiving element.

As noted above, silver transfer images formed in regenerated cellulose exhibit advantageous handling and stability characteristics. Particularly good image stability properties are obtained when the process is performed using a hydroxylamine silver halide developing agent and an organic silver halide solvent, the resulting silver transfer images exhibiting exceptional stability without requiring washing or print coating. It has been found, however, that longer imbibition times may be necessary to reach a desired maximum density, e.g., a density of about 1.4 to 1.6, than is the case with prior silver transfer processes employing benzenoid silver halide developing agents and inorganic silver halide solvents. Apart from the possible inconvenience of a somewhat longer inbibition period (e.g., 30 to 45 seconds as compared with 10 to 15 seconds for the prior print-coated silver transfer process) it has been found that a higher minimum density is obtained in the regenerated cellulose imagereceiving element'than is obtained in the now conventional print-coated silver transfer image using the same silver halide emulsion. It is believed that this undesirable higher minimum density results, at least in part, from a longer induction period for developing exposed (negative) silver halide frequently exhibited by hydroxylamine silver halide developing agents as compared with benzenoid silver halide developing agents. In such instances, the silver halide solvent may dissolve and transfer silver halide grains that would have been developed with a shorter induction period developing agent, thereby increasing highlight density. It has now been found that undesired minimum density may be avoided by employing a silver halide emulsion having particular silver halide grain characteristics as hereinafter set forth in detail.

Hydroxylamine silver halide developing agents, as noted above, have been found to be particularly useful in forming silver transfer images which require little or no after treatment, especially when used in combination with regenerated cellulose silver receptive strata. Particularly useful hydroxylamine silver halide developing agents are the N-alkyl and N-alkoxyalkyl substituted hydroxylamines. A large number of such hydroxylamines are described in U. S. Pat. Nos. 2,857,274, 2,857,275 2,857,276, 3,287,124, 3,287,125 and 3,293,034. Particularly effective and preferred hydroxylamine silver halide developing agents may be described by the formula wherein R is alkyl, alkoxyalkyl or alkoxyalkoxyalkyl, and R is hydrogen, alkyl, alkoxyalkyl, alkoxyalkoxyalkyl or alkenyl. The alkyl, alkoxy and alkenyl. radicals preferably contain from one to three carbons. Particularly useful hydroxylamine silver halide developing agents include N,N-diethyl-hydroxylamine, N,N-bismethoxyethyl-hydroxylamine and N,N-bis-ethoxyethylhydroxylamine.

The silver halide solvent may be an alkali metal thiosulfate, e.g., sodium or potassium thiosulfate, and preferably is a cyclic imide of the type discussed in detail in the aforementioned U.S. Pat. Nos. 3,857,274, 2,857,275 and 3,857,276, e.g., uracil, urazole, 5- methyl-uracil, etc.

The processing composition includes an alkali, preferably an alkali metal hydroxide such as sodium or potassium hydroxide. If the processing composition is applied by being distributed as a thin layer between the superposed photosensitive ad image-receiving elements, and particularly if so distributed as said elements, are brought into superposed relationship, the processing composition preferably includes a polymeric film-forming, thickening or viscosity-providing agent. I-Iydroxyethyl cellulose and sodium carboxymethyl cellulose are particularly useful for this purpose, and are included in the processing composition in concentrations effective to provide the appropriate viscosity in accordance with principles well-known in diffusion transfer photography. The processing composition may also include other additives, as is conventional in silver transfer processes, such as anitfoggants, toning agents, stabilizing agents, etc. In particular, it has been found useful to include an oxyethylamino compound, such as triethanolamine, to increase the processing composition shelf life as disclosed and claimed in the copending application of Sidney Kasman, Ser. No. 725,145 filed Apr. 29, 1968 (now U. S. Pat. No. 3,619,185 issued Nov. 9, 1971).

The image-receiving element comprises a support, such as baryta paper, cellulose triacetate or a polyester, carrying a layer of regenerated cellulose containing a silver precipitating agent. Such image-receiving elements may be prepared by applying a coating solution of an appropriate cellulose ester, such as cellulose diacetate, containing a silver precipitating agent dispersed therein, to a support, suitably subcoated if necessary. The resulting layer of cellulose ester is subjected to alkaline hydrolysis to convert at least a depthwise portion of the cellulose ester to cellulose. In particularly useful embodiments, the unhydrolyzed portion of the cellulose ester layer containing a silver precipitating agent and/or an underlying unhydrolyzed cellulose ester, e.g., cellulose diacetate, contain one or more mercapto compounds adapted to improve the tone, stability, or other photographic property of the silver transfer image; such mercapto compounds are made available during imbibition by diffusion from their initial location. Image-receiving elements of this type are disclosed and claimed in the copending application of Richard W. Young, Ser. No. 717,683 filed Apr. 1, 1968 (now U. S. Pat. No. 3,607,269 issued Sept. 21, 1971).

Examples of suitable silver precipitating agents include heavy metals such as iron, lead, zinc, nickel, cadmium, tin, chromium, copper, cobalt, particularly noble metals such as gold, silver, platinum and palladium. Other useful silver precipitating agents include sulfides and selenides of heavy metals, particularly: sulfides of mercury, copper, aluminum, zinc, cadmium, cobalt, nickel, silver, lead, antimony, bismuth, cerium and magnesium; and selenides of lead, zinc, antimony and nickel. The function of such materials as silver precipitating agents in a silver transfer process is described, for example, in U.S. Pat. No. 2,774,667, issued on Dec. 18, 1956 in the names of Edwin H. Land et al.

The silver halide emulsions found to give improved minimum density silver transfer images in accordance with this invention comprise silver bromide, silver iodobromide or other mixed halide emulsions wherein the silver halide is substantially completely in the form of silver halide grains having a diameter of at least 0.5 micron, i.e., at least and preferably at least 99%, of the silver halide grains have a diameter of at least 0.5 micron.

Grain size distribution curves, or grain size-frequency distribution curves as they are sometimes called, are frequently used to describe and define silver halide emulsions. Mees and James, The Theory of the Photographic Process, 3rd Edition, The Macmillan Company, New York, N.Y. 1966, pages 36-44, set forth a description of techniques of measuring the size of silver halide grains and of determining the frequency of grains of given sizes in a particular silver halide emulsion. Electron microscope size-frequency analysis of silver halide emulsions gives very high accuracy measurements, particularly of grains below the resolution of light microscopy but is a relatively slow procedure. More rapid size-frequency analysis procedures utilize an analyzer or counter, and calculate the particle sizefrequency distribution from the measurements of the number of grains of specific sizes, assuming a log normal distribution (see page 39 of Mees and James, cited above), and the resulting graph therefore reflects in assumed measurements, i.e., grain sizes below the resolving capability of the measuring device. FIG. 1 reproduces the grain size distribution curves for two silver halide emulsions, plotted assuming a log normal distribution using particle size data obtained with a Coulter counter having a minimum grain size. measurement of 0.47 micron. (The horizontal axis represents diameter in micron while the vertical axis represents the relative number of grains.) The solid curve A is a grain size distribution curve for a silver iodobromide emulsion (hereinafter referred to as Emulsion A) characterized by having a substantial, if not major, proportion of the silver in the form of silver halide grains less than 0.5 micron in diameter; this silver halide emulsion was found to give good minimum density in the conventional diffusion transfer process using a benzenoid silver halide developing agent but an undersirably high minimum density when a cellulose receiving layer was used in combination with a hydroxylamine silver halide developing agent. In contrast, a good minimum density was obtained in the latter process using the silver halide emulsion (hereinafter referred to as Emulsion B) having the grain size distribution depicted in curve B and wherein substantially all of the silver is present of the form of grains having a diameter of approximately 0.5 micron and larger. Assuming a log normal distribution, approximately 41.3% of the grains of Emulsion A and 3.1% of the grains of Emulsion B were smaller than 0.47 micron. Applying the same log normal distribution assumption, approximately 3.0% of the silver in Emulsion A and 0.12% of the silver in Emulsion B was present in the form of grains having a diameter smaller than 0.47 micron.

FIGS. 2 and 3 depict grain size distribution curves N of data obtained by electron microscopy for different samples of the above Emulsions A and B, respectively, as well as area curves NA and volume curves NV for the same emulsions. The horizontal axis for each of the curves in FIGS. 2 and 3 represents relative log diameter of the silver halide grains, while the vertical axis represents the number of grains normalized, with the dotted curves representing cumulative percentile; the 0.5 micron point as marked on the horizontal axes and the 50th percentile point is marked on the vertical axes. The NA curves depict how much of the total area covered is represented by grains of a given size, while the NV curves depict how much of the total silver present is represented by grains of a given size. The cumulative percentile values for N, Na And NV for representative grain diameters of Emulsions A and B found in the electron microscopy analysis were:

These figures clearly demonstrate the fact that the silver of Emulsion B is substantially completely in the form of grains having a diameter of more than 0.5 micron.

Each of Emulsion A and Emulsion B are gelatino silver iodobromide emulsions containing 6 mole percent iodide, with a gelatin to silver ratio of 2.5. The emulsions were coated at levels of approximately 100 mg. of silver per square foot.

in addition to obtaining silver transfer images exhibiting lower minimum density, it has been found that lower concentrations of silver precipitating agents are required to obtain a given maximum density, e.g., 1.4 to 1.6, using silver halide emulsions having the grain characteristics defined above, such as Emulsion B, than are necessary when using emulsions having a substantial number of grains smaller than 0.5 micron in diameter, such as Emulsion A.

The following examples are intended to be illustrative of this invention and are not intended to be limiting.

EXAMPLE 1 Emulsion B defined above was coated on a support to provide a silver coverage of approximately 99 mg.

per square foot. The resulting photosensitive element was photoexposed and then diffusion transfer processed by distributing a layer 0.0028 inch thick of a processing composition between said photoexposed silver halide emulsion and a regenerated cellulose imagereceiving element. The processing composition comprised:

Potassium hydroxide (aqueous solution 45% KOH) 323 cc. Titanium dioxide 3 g. l-lydroxyethyl cellulose 79 g. Zinc oxide 9.75 g. N,N-bis-methoxyethylhydroxylamine g. Triethanolamine solution (4.5 parts triethanolamine to 6.2 parts water) 17.14 g. Tetrahydropyrimidine thione 0.4 g. 2,4-dimercaptopyrimidine 0.35 g. Uracil g. Water 1193 cc.

The image-receiving element was prepared by coating baryta paper with a 0.25 mil layer of cellulose diacetate (2.4 DS) containing mg. per square foot of 1,6-bis- (5-mercapto-1,3 ,4-thiadizaolyl-2-thio)-hexane followed by a 0.2 mil layer of cellulose diacetate (2.4 DS) containing colloidal nickel sulfide as silver precipitating agent and 50 mg. per square foot of 1,6-bis-(5- mercapto-1,3 ,4-thiadiazolyl-2-thio-hexane, after which the outer cellulose acetate layer was hydrolyzed to regenerated cellulose to a depth of approximately 0.075 mil. After a 30 second inbibition, the image-receiving element was separated and contained a high quality silver transfer image with a maximum density of 1.48 and a minimum density of 0.04, with a Diffusion Transfer Equivalent Exposure Index of 3400.

EXAMPLE 2 The process set forth in Example 1 was repeated, replacing the tetrahydropyrimidine thione with 0.15g'. per liter of imidazolidine-Z-thione. The resulting silver transfer image exhibited comparable minimum and maximum densities, a more neutral tone and higher contrast compared with the silver transfer image obtained in Example 1.

EXAMPLE 3 For comparison purposes, a photosensitive element having silver halide Emulsion A coated at .approximately 100 mg. per square foot was processed in the same manner as described in Example 1. The resulting silver transfer image also had a minimum density of 0.04 but the maximum density had dropped to 1.22 and the Diffusion Transfer Equivalent Exposure Index was 2900. By increasing the nickel sulfide concentration in the image-receiving layer three-fold, the maximum density of the silver transfer image was increased to the level obtained in Example 1 but the minimum density almost doubled to 0.07. This comparison illustrates the reduction in minimum density obtained without loss of maximum density by use of a silver halide emulsion having the silver halide substantially completely in the form of grains having a diameter of at least 0.5 micron.

It will be understood that transparent supports may be employed in lieu of paper supports where it is desired to have transparencies which may be viewed by transmitted light or by projection. It is also within the scope of this invention to use a translucent support, e.g., a cellulose acetate support which has been ocated with a translucent layer of titanium dioxide. Use of a translucent support permits the transfer image to be viewed by reflected or transmitted light.

Application of a thin strip coat, e.g., of dimethyl hydantoin formaldehyde or gum arabic, to the surface of the hydrolyzed image-receiving layer has been found to be helpful in preventing or minimizing adhesion of the solidified layer of processing composition to the imagereceiving element upon separation of the superposed elements. If desired, the strip coat may also serve as a carrier for a reagent, e.g., a toning agent; in that event, a portion of such reagent may also diffuse inwardly into the hydrolyzed layer.

It has been noted that the photographic processing solution is effective to extract alkali-soluble reagents from the unhydrolyzed polymer and diffuse them into the hydrolyzed stratum during photographic processing. it is also possible to effect a redistribution of such alkali-soluble reagents from the unhydrolyzed to the hydrolyzed stratum prior to photographic processing by briefly contacting the image-receiving element with a solution such as aqueous methanol, with or without an alkali also being present.

Mercapto-thiadiazoles, e.g., Z-acetamido-S-mercapto-l ,3,4-thiadiazole and 1,6-bis-(-mercapto-1,3 ,4- thiadiazolyl-Z-thio )-hexane, give unexpectedly superior results in increasing the stability of silver transfer images to attack, and especially to attack by sulfur.

It will be noted that where the pre-imbibition hydrolysis is of only a portion of the image-receiving layer, the silver precipitating nuclei are present in both the hydrolyzed and unhydrolyzed portions of this layer. Examination of photomicrographs of cross-sections of such partially hydrolyzed cellulose acetate receiving layers has shown that the transfer image silver is deposited only in the pre-imbibition hydrolyzed portion, even though a substantial portion of the originally unhydrolyzed cellulose acetate may be hydrolyzed by a secondary hydrolysis during imbibition and silver precipitating nuclei thus made available deeper in the imagereceiving element. It has been found that good results can be obtained where the cellulose acetate has been hydrolyzed to a depth of about 0.00002 to 0.00015 inches, the total thickness of the hydrolyzed and unhydrolyzed portions being about 0.00010 to 0.00050 inches, these thicknesses being measured after hydrolysis (and prior to diffusion transfer processing) since some shrinking of the original coated thickness will occur as a result of the hydrolysis and subsequent heat drying. in the most useful embodiments, the hydrolyzed portion is about 0.00004 to 0.00010 inches and the total thickness of the hydrolyzed and unhydrolyzed portions is about 0.00015 to 0.00030 inches. The total thickness prior to hydrolysis may be about 0.00015 to 0.00060 inches, and preferably about 0.00020 to 0.00030 inches.

As is well known in the art, silver precipitants are present in very low quantities, e.g., about 1 to 25 X moles per square foot. The lowest possible levels are usually used, as higher concentrations may cause excessive silver deposition or undesirable background density in the highlight areas. Mixtures of silver precipitants may be used. The image-receiving layer thus may be described as substantially colorless and substantially transparent insofar as the presence of the nuclei is concerned.

As noted above, where the hydrolyzed polymer exhibits an adhesive tendency towards the solidified layer of processing fluid, e.g., as may occur where the surface of the image-receiving element is converted to cellulose and the processing fluid contains a film-forming polymer such as sodium carboxymethyl cellulose or hydrolyzed surface with a suitable stripping layer to facilitate separation of the image-receiving element from the layer of processing fluid. Materials suitable for providing a stripping layer are well known in the art, and are exemplified by materials such as cellulose acetate hydrogen phthalate as well as others mentioned above. it will be appreciated, however, that in some instances it may be desirable to have the solidified layer of processing fluid preferentially adhere to the surface of such an image-receiving layer, in which event such a stripping layer should be omitted.

Additive color images may be formed by forming the silver transfer image in accordance with this invention, said image being in registered relationship with an additive color screen. In such embodiments, the additive color screen is preferably positioned between a transparent support and said silver-receptive stratum, exposure of the silver halide emulsion being effected through said screen.

It is also contemplated to utilize the techniques of this invention in high covering power transfer processes of the type disclosed in U. S. Pat. No. 2,861,885 issued Nov. 25, 1958 to Edwin H. Land, wherein the positive transfer image may be maintained in superposed relationship with the developed silver halide layer and viewed as a positive image.

It is also contemplated that the silver halide emulsion may be coated over the image-receptive stratum, the silver halide emulsion being removable after processing, as by provision of a suitable stripping layer or by employment of a silver halide emulsion which may be readily washed off after processing, e.g., a silver halide emulsion wherein the binder is cellulose acetate hydrogen phthalate. Alternatively, a pigmented layer, e.g., titanium dioxide in gelatin or a suitable plastic, may be positioned between the silver halide emulsion and the silver-receptive stratum coated on a transparent base, and the silver transfer image viewed through the transparent base against the pigmented layer, the pigmented layer masking out the image in the developed silver halide emulsion layer.

Since certain changes may be made in the above products and processes without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is: g

1. The method of forming asilver transfer image comprising exosing a photosensitive silver halide emulsion, developing said exposed silver halide emulsion with an aqueous alkaline processing solution including a hydroxylamine silver halide developing agent and a silver halide solvent, forming an imagewise distribution of a diffusible silver complex as a function of said development, transferring at least a portion of said imagewise distribution of diffusible silver complex to a superposed silver receptive stratum of regenerated cellulose containing a silver precipitating agent to form said silver transfer image, the silver halide of said silver halide emulsion being substantially completely in the form of grains having a diameter of at least 0.5 micron.

2. The method as defined in claim 1 wherein less than 1% of said silver halide grains have a diameter less than 0.5 micron.

3. The method as defined in claim 1 wherein said silver halide developing agent is an N,N-bis-alkoxyalkylhydroxylamine wherein each of said alkoxy and alkyl radicals contain from one to three carbons.

4. The method as defined in claim 1 wherein said silver halide solvent is an organic silver halide solvent.

5. The method as defined in claim 4 wherein silver halide solvent is a cyclic imide.

6. The method as defined in claim 5 wherein said cyclic imide is uracil.

7. The method as defined in claim 1 wherein said stratum of regenerated cellulose is contiguous with a stratum of an alkali-hydrolyzable cellulose ester containing a mercapto-substituted compound, at least a portion of said mercapto-substituted compound being diffused to said stratum of regenerated cellulose during the formation of said silver transfer image.

8. The method as defined in claim 7 wherein said stratum of cellulose ester also contains a silver precipitating agent.

9. The method as defined in claim 7 wherein said silver halide developing agent is an N,N-dialky1 substituted hydroxylamine and said silver halide solvent is a cyclic imide.

10. The method as defined in claim 7 wherein said mercapto-substituted compound is effective to increase the stability of said silver transfer image.

11. The method as defined in claim 10 wherein said mercapto-substituted compound is a mercaptothiadiazole.

12. The method as defined in claim 1 wherein said silver precipitating agent is a colloidal metal sulfide.

13. A diffusion transfer film unit comprising a photosensitive silver halide emulsion in which the silver halide is substantially completely in the form of grains having a diameter greater than 0.5 microns, an image receiving layer comprising a stratum of regenerated cellulose containing a silver precipitating agent, and a processing composition comprising an aqueous alkaline solution, said film unit including a hydroxylamine silver halide developing agent and a silver halide solvent, said photosensitive silver halide emulsion and said image receiving layer being carried by a single support or being carried by separate superposable supports.

14. A film unit as defined in claim 13 wherein less than 1% of the silver halide grains of said silver halide emulsion have a diameter less than 0.5 microns.

15. A film unit as defined in claim 14 wherein said silver halide solvent is an organic silver halide solvent.

16. A film unit as defined in claim 15 wherein said silver halide solvent is a cyclic imide.

17. A film unit as defined in claim 16 wherein said cyclic imide is uracil.

18. A film unit as defined in claim 13 wherein said silver halide developing agent is an N,N-bis-alkoxyalkylhydroxylamine wherein each of the alkoxy and alkyl radicals contains from one to three carbon atoms.

19. A film unit as defined in claim 13 wherein said stratum of regenerated cellulose is contiguous with a stratum of an alkali hydrolysable cellulose ester positioned between said regenerated cellulose stratum and the support carrying said regenerated cellulose straturn.

20. A film unit as defined in claim 19 wherein said stratum of alkali hydrolysable cellulose ester contains a diffusible mercapto substituted compound.

21. A film unit as defined in claim 20 wherein said mercapto substituted compound is a mercaptothiadiazole.

22. A film unit as defined in claim 19 wherein said stratum of alkali hydrolysable cellulose ester contains a silver precipitating agent.

23. A film unit as defined in claim 22 wherein said silver precipitating agent is a colloidal metal sulfide.

24. A diffusion transfer film unit comprising a first support carrying a photosensitive silver halide emulsion wherein less than 1% of the silver halide grains have a diameter less than 0.5 microns, a second support carrying an image receiving layer comprising a stratum of regenerated cellulose containing silver precipitating agent contiguous with a stratum of alkali hydrolysable cellulose ester, and a rupturable container releasably holding a processing composition comprising an aqueous alkaline solution, an N,N-dialkyl substituted hydroxylamine silver halide developing agent and an organic silver halide solvent, said rupturable container being so positioned as to discharge its contents for distribution between said silver halide emulsion and said image-receiving layer.

Patent No. 3,765,889 Dated October 1 1973 Inventor(s) Richard W. Y ounq It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1," line 12, "precipitatinG" should be --precipitating--.

Column 1, line 16, "regeneratd" should be --regenerated-. Column 2, line 42, "inhibition" should be --imbibition.

Column 3 line 30, "ad" should be -and-'.

Column 4, line 46, after "in" insert --part.

Column 5., line 28, "Na And should be ---,NA and-.

Column 5, line 38, in table, column under B, "0.07" should be O.70--.

Column 6, line 20, "thiadizaolyl" should be --thiadiazolyl-.

Column 6, line 65, "ocated' should be -coated.

Signed and sealed this 5th day of November 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents FORM PO-IOSO (10-69) USCOMM-DC OOB'IG-PGQ r us. oovrnunlur murmur. omc: ID, o-au-n: 

2. The method as defined in claim 1 wherein less than 1% of said silver halide grains have a diameter less than 0.5 micron.
 3. The method as defined in claim 1 wherein said silver halide developing agent is an N,N-bis-alkoxyalkylhydroxylamine wherein each of said alkoxy and alkyl radicals contain from one to three carbons.
 4. The method as defined in claim 1 wherein said silver halide solvent is an organic silver halide solvent.
 5. The method as defined in claim 4 wherein silver halide solvent is a cyclic imide.
 6. The method as defined in claim 5 wherein said cyclic imide is uracil.
 7. The method as defined in claim 1 wherein said stratum of regenerated cellulose is contiguous with a stratum of an alkali-hydrolyzable cellulose ester containing a mercapto-substituted compound, at least a portion of said mercapto-substituted compound being diffused to said stratum of regenerated cellulose during the formation of said silver transfer image.
 8. The method as defined in claim 7 wherein said stratum of cellulose ester also contains a silver precipitating agent.
 9. The method as defined in claim 7 wherein said silver halide developing agent is an N,N-dialkyl substituted hydroxylamine and said silver halide solvent is a cyclic imide.
 10. The method as defined in claim 7 wherein said mercapto-substituted compound is effective to increase the stability of said silver transfer image.
 11. The method as defined in claim 10 wherein said mercapto-substituted compound is a mercapto-thiadiazole.
 12. The method as defined in claim 1 wherein said silver precipitating agent is a colloidal metal sulfide.
 13. A diffusion transfer film unit comprising a photosensitive silver halide emulsion in which the silver halide is substantially completely in the form of grains having a diameter greater than 0.5 microns, an image receiving layer comprising a stratum of regenerated cellulose containing a silver precipitating agent, and a processing composition comprising an aqueous alkaline solution, said film unit including a hydroxylamine silver halide developing agent and a silver halide solvent, said photosensitive silver halide emulsion and said image receiving layer being carried by a single support or being carried by separate superposable supports.
 14. A film unit as defined in claim 13 wherein less than 1% of the silver halide grains of said silver halide emulsion have a diameter less than 0.5 microns.
 15. A film unit as defined in claim 14 wherein said silver halide solvent is an organic silver halide solvent.
 16. A film unit as defined in claim 15 wherein said silver halide solvent is a cyclic imide.
 17. A film unit as defined in claim 16 wherein said cyclic imide is uracil.
 18. A film unit as defined in claim 13 wherein said silver halide developing agent is an N,N-bis-alkoxyalkylhydroxylamine wherein each of the alkoxy and alkyl radicals contains from one to three carbon atoms.
 19. A film unit as defined in claim 13 wherein said stratum of regenerated cellulose is contiguous with a stratum of an alkali hydrolysable cellulose ester positioned between said regenerated cellulose stratum and the support carrying said regenerated cellulose stratum.
 20. A film unit as defined in claim 19 wherein said stratum of alkali hydrolysable cellulose ester contains a diffusible mercapto substituted compound.
 21. A film unit as defined in claim 20 wherein said mercapto substituted compound is a mercapto-thiadiazole.
 22. A film unit as defined in claim 19 wherein said stratum of alkali hydrolysable cellulose ester contains a silver precipitating agent.
 23. A film unit as defined in claim 22 wherein said silver precipitating agent is a colloidal metal sulfide.
 24. A diffusion transfer film unit comprising a first support carrying a photosensitive silver halide emulsion wherein less than 1% of the silver halide grains have a diameter less than 0.5 microns, a second support carrying an image receiving layer comprising a stratum of regenerated cellulose containing silver precipitating agent contiguous with a stratum of alkali hydrolysable cellulose ester, and a rupturable container releasably holding a processing composition comprising an aqueous alkaline solution, an N,N-dialkyl substituted hydroxylamine silver halide developing agent and an organic silver halide solvent, said rupturable container being so positioned as to discharge its contents for distribution between said silver halide emulsion and said image-receiving layer. 